Syringes are used to expel a fluid through an orifice, such through a nozzle, or tubing, or cannula, such as a hypodermic needle.
FIG. 3 of the drawings shows, in phantom, a side elevation view of a common syringe 80. Syringe 80 generally includes a barrel 81 and a plunger 90. Barrel 81 includes walls 82 forming a tube surrounding a lumen 83 for holding the fluid, a closed front end 84 including an orifice 85 for expelling the fluid, and an open rear end 87 defining a rear orifice 88 and having an outwardly extending flange 89 around rear orifice 88. Front orifice 85 typically includes an attachment or collar 86 for attachment of a hypodermic needle, tubing, or nozzle 99.
Plunger 90 includes a front end 91 disposed in lumen 83 of barrel 81, a midsection 93 disposed in rear orifice 88 of barrel 81, and a rear end 94 including a rear-facing, bearing surface 95. Front end 91 may have a seal, such as O-ring 92 for sealing between plunger 90 and barrel walls 82. Syringe 80 has a horizontal center axis 96 midway between the top and bottom of the syringe.
Typically, in use, barrel 81 is held with one hand while fingers of the other hand are placed on the front of flange 89 and the thumb of the other hand is placed on bearing surface 95 of plunger 94. The finger and thumb are squeezed together to force plunger 90 further into barrel 81 to expel the fluid.
Mixing syringes have two or more separate lumens for holding reactive components, that is, components that must be mixed in a precise ration and that change their chemical or physical nature upon mixing. It is common to design the mixing syringe such that pressing plunger 90 dispenses all components simultaneously in the correct ratio. The components begin mixing as they exit their respective nozzles. Two-part epoxy is often packaged in such mixing syringes.
One problem with conventional mixing syringes is that care must be taken to depress plunger 90 without applying more pressure to one side than the other so that the ration is correct.
Another problem with mixing syringes is that they often require a large force to expel. Exerting the required force is difficult or impossible for some persons, and it may be difficult to exert the force uniformly during the plunger stroke to evenly distribute the output.
Therefore, there has been a need for a device to aid in the use of mixing syringes.
The safe and effective administration of many types of hypodermic injections by syringe requires sensitive tactile feedback to the administrator. This necessity for tactile feed back is well-know with regard to epidural injections. In epidural injections, the administration attempts to keep a constant force on the plunger while detecting changes in resistance to the flow of fluid. If the resistance goes up, it is a sign that further injection of fluid may cause damage to the patient. Therefore, the administrator is very careful not to exceed the desired force, until the fluid already injected dissipates and the force decreases to the desired force or the administrator moves the tip of the needle slightly to find a more accepting location such that the force decreases to the desired force. Additionally, the force to the plunger must be applied axially or the apparent resistance increases. It is difficult to apply a purely axial force over the long period of time required for some injections, so false feedback is common.
Therefore, there is a need for a device that aids in providing accurate, sensitive tactile feedback to the administrator of an injection with a syringe.